U.S. patent application number 13/585706 was filed with the patent office on 2015-01-15 for transmit/receive unit, and methods and apparatus for transmitting signals between transmit/receive units.
This patent application is currently assigned to ADVANTEST (SINGAPORE) PTE LTD. The applicant listed for this patent is Edmundo de la Puente, David D. Eskeldson. Invention is credited to Edmundo de la Puente, David D. Eskeldson.
Application Number | 20150015284 13/585706 |
Document ID | / |
Family ID | 40985957 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150015284 |
Kind Code |
A1 |
de la Puente; Edmundo ; et
al. |
January 15, 2015 |
TRANSMIT/RECEIVE UNIT, AND METHODS AND APPARATUS FOR TRANSMITTING
SIGNALS BETWEEN TRANSMIT/RECEIVE UNITS
Abstract
In one embodiment, apparatus for transmitting and receiving data
includes a transmission line network having at least three
input/output terminals; at least three transmit/receive units,
respectively coupled to the at least three input/output terminals;
and a control system. The control system is configured to,
depending on a desired direction of data flow over the transmission
line network, i) dynamically place each of the transmit/receive
units in a transmit mode or a receive mode, and ii) dynamically
enable and disable an active termination of each transmit/receive
unit. Methods for using this and other related apparatus to
transmit and receive data over a transmission line network are also
disclosed.
Inventors: |
de la Puente; Edmundo;
(Cupertino, CA) ; Eskeldson; David D.; (Colorado
Springs, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
de la Puente; Edmundo
Eskeldson; David D. |
Cupertino
Colorado Springs |
CA
CO |
US
US |
|
|
Assignee: |
ADVANTEST (SINGAPORE) PTE
LTD
Singapore
SG
|
Family ID: |
40985957 |
Appl. No.: |
13/585706 |
Filed: |
August 14, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12276299 |
Nov 21, 2008 |
8242796 |
|
|
13585706 |
|
|
|
|
12035378 |
Feb 21, 2008 |
8384410 |
|
|
12276299 |
|
|
|
|
Current U.S.
Class: |
324/750.3 |
Current CPC
Class: |
H04L 25/028 20130101;
H04B 3/46 20130101; H04B 1/40 20130101; H04L 25/0278 20130101 |
Class at
Publication: |
324/750.3 |
International
Class: |
H04B 3/46 20060101
H04B003/46; H04B 1/40 20060101 H04B001/40 |
Claims
1. A method for transmitting signals between at least three
transmit/receive units coupled to a transmission line network, the
method comprising: for each signal transmission over the
transmission line network, designating one of the transmit/receive
units as a transmitting unit and designating all other ones of the
transmit/receive units as non-transmitting units, for each of at
least two different signal transmissions over the transmission line
network, designating a different one of the transmit/receive units
as the transmitting unit; using at least one of the
non-transmitting units, actively terminating the transmission line
network by driving a DC voltage through an active driver of each of
the at least one non-transmitting unit, the active driver having an
output that is coupled to the transmission line network via a
termination resistor; from the transmitting unit, transmitting a
signal over the transmission line network; and receiving the
transmitted signal at one or more of the non-transmitting
units.
2. The method of claim 1, further comprising, for each of the at
least two different signal transmissions over the transmission line
network: actively terminating the transmission line network by
driving a DC voltage through an active driver of each
non-transmitting unit coupled to the transmission line network.
3. Apparatus for transmitting and receiving data, comprising: a
transmission line network having at least three input/output
terminals; at least three transmit/receive units, respectively
coupled to the at least three input/output terminals, each of the
transmit/receive units having i) an active receiver having a
receiver input coupled to a respective one of the input/output
terminals; ii) an active driver having a driver input coupled to a
driver output; iii) a termination resistor coupling the driver
output to a respective one of the input/output terminals; and iv) a
switching element configured to selectively couple the driver input
to a DC voltage source.
4. The apparatus of claim 3, wherein the switching element is
further configured to selectively couple the driver input to a
signal source, the apparatus further comprising: a control system
coupled to the switching elements of the at least three
transmit/receive units, the control system configuring the
switching elements of the transmit/receive units to A) couple the
driver input and the signal source of a transmitting one of the
transmit/receive units, and B) couple the driver input and DC
voltage source of at least one non-transmitting one of the
transmit/receive units.
5. The apparatus of claim 3, wherein for each of the
transmit/receive units, the switching element of the respective
transmit/receive unit comprises: a multiplexer having first and
second multiplexer inputs, a multiplexer output coupled to the
driver input, and a select input; wherein the DC voltage source is
coupled to the first multiplexer input and the signal source is
coupled to the second multiplexer input.
6. The apparatus of claim 5, further comprising: a control system
coupled to the select inputs of the multiplexers, the control
system configuring the multiplexers to A) couple the driver input
and the signal source of a transmitting one of the transmit/receive
units, and B) couple the driver input and the DC voltage source of
other ones of the transmit/receive units.
7. The apparatus of claim 3, wherein the at least three
transmit/receive units consist of three transmit/receive units.
8. The apparatus of claim 3, wherein the transmission line network
comprises three transmission line segments, each of the
transmission line segments having first and second ends, wherein
the first ends of the transmission line segments are coupled to
respective ones of the transmit/receive units, and wherein the
second ends of the transmission line segments are coupled to one
another at a common branching node.
9. The apparatus of claim 8, wherein each of the three transmission
lines has a characteristic impedance of 50 Ohms.
10. The apparatus of claim 3, wherein the transmission line network
defines a 1:2 signal fan-out from a first one of the
transmit/receive units to second and third ones of the
transmit/receive units.
11. The apparatus of claim 10, further comprising: a first
adjustable delay element coupled to a receiver output of the active
receiver of the second transmit/receive unit; a second adjustable
delay element coupled to a receiver output of the active receiver
of the third transmit/receive unit; and a delay controller
configured to adjust delays of the first and second adjustable
delay elements.
12. The apparatus of claim 3, wherein the active driver of a first
one of the transmit/receive units is configured to transmit signals
carrying timing and voltage information over the transmission line
network, and wherein the transmission line network is configured to
split the signals and provide the signals to second and third ones
of the transmit/receive units.
13. The apparatus of claim 3, wherein first and second ones of the
transmit/receive units are configured to transmit signals carrying
timing and voltage information over the transmission line network,
and wherein the transmission line network is configured to provide
the signals driven by the first and second ones of the
transmit/receive units to a third one of the transmit/receive
units.
14. Apparatus for transmitting and receiving data, comprising: a
transmission line network having at least three input/output
terminals; at least three transmit/receive units, respectively
coupled to the at least three input/output terminals; and a control
system configured to, depending on a desired direction of data flow
over the transmission line network, i) dynamically place each of
the transmit/receive units in a transmit mode or a receive mode,
and ii) dynamically enable and disable an active termination of
each transmit/receive unit.
15. The apparatus of claim 14, further comprising a test system,
the test system having a test channel in which the at least three
transmit/receive units are incorporated, the at least three
transmit/receive units defining a 1:2 fan-out of the test
channel.
16. The apparatus of claim 15, wherein the test system comprises a
plurality of the test channels.
17. Apparatus for transmitting and receiving data, comprising: a
transmit/receive unit having i) an input/output terminal; ii) an
active receiver having a receiver input coupled to the input/output
terminal; ii) an active driver having a driver input coupled to a
driver output; iii) a termination resistor coupling the driver
output to the input/output terminal; and iv) a switching element
configured to selectively couple the driver input to i) a DC
voltage source, and alternately, ii) a signal source.
18. The apparatus of claim 17, wherein the switching element
comprises a multiplexer having first and second multiplexer inputs,
a multiplexer output coupled to the driver input, and a select
input; wherein the DC voltage source is coupled to the first
multiplexer input and the signal source is coupled to the second
multiplexer input.
19. The apparatus of claim 17, further comprising an adjustable
delay element coupled to a receiver output of the active receiver.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of the U.S.
patent application of De La Puente et al. entitled "Parallel Test
Circuit with Active Devices" (application Ser. No. 12/035,378,
filed Feb. 21, 2008), which application is hereby incorporated by
reference for all that it discloses. The application Ser. No.
12/035,378 application is referred to herein as the '378
application.
BACKGROUND
[0002] The '378 application discloses a parallel test circuit with
active devices. A high-level representation of an exemplary one of
the parallel test circuits disclosed in the '378 application is
shown in FIG. 7. The parallel test circuit 700 utilizes a channel
input/output (I/O or IO) block 702 and four DUT I/O blocks 704,
706, 708, 710 to fan-out/fan-in a signal by four (i.e., 1:4 or 4:1)
between a TESTER_IO node and four DUT_IO nodes (DUT_IO.sub.--0,
DUT_IO.sub.--1, DUT_IO.sub.--2 and DUT_IO.sub.--3).
[0003] Each of the channel and DUT I/O blocks 702, 704, 706, 708,
710 comprises an active driver and an active receiver. The labeling
of which is which (i.e., which are drivers and which are receivers)
is largely a matter of choice. In FIG. 7, the elements that move
signals away from the TESTER_IO node, toward one or more of the
DUT_IO nodes, are referred to as "drivers". The elements that move
signals away from one or more of the DUT_IO nodes, toward the
TESTER_IO node, are referred to as "receivers". With this
convention in mind, the channel I/O block 702 comprises an active
driver 712, an active receiver 714, and a termination resistor 716.
The input of the active driver 712 is coupled to the TESTER_IO
node, and the output of the active driver 712 is coupled to the
inputs of active drivers 718, 720, 722, 724 in each of the DUT I/O
blocks 704, 706, 708, 710. Via a multiplexer 726, the input of the
active receiver 714 is selectively coupled to the outputs of active
receivers 728, 730, 732, 734 in each of the DUT I/O blocks 704,
706, 708, 710. The output of the active receiver 714 is coupled to
the TESTER_IO node via the termination resistor 716.
[0004] Each of the DUT I/O blocks 704, 706, 708, 710 comprises an
active driver (e.g., driver 718), an active receiver (e.g.,
receiver 728), and a termination resistor (e.g., resistor 736). The
output of the active driver in each DUT I/O block is coupled, via a
respective termination resistor, to one of the plurality of DUT_IO
nodes. Also coupled to each of the DUT IO nodes is a respective
input of one of the active receivers.
[0005] In operation, a signal received at the TESTER_IO node of the
parallel test circuit 700 may be fanned out to any or all of the
DUT_IO nodes, or signals read at any of the DUT_IO nodes may be
selectively transmitted back to the TESTER_IO node. In some cases,
and as described in the '378 application, the parallel test circuit
700 may be augmented to provide for parallel reads from the DUT_IO
nodes.
[0006] In theory, the parallel test circuits described in the '378
application can be expanded by coupling a single channel I/O block
702 to increasing numbers of DUT I/O blocks 704, 706, 708, 710,
thereby increasing signal fan-out/fan-in by any number of signal
paths (e.g., by 4, by 8, or by any other number of signal paths).
In practice, however, it becomes more difficult to maintain signal
integrity and DUT isolation as the fan-out/fan-in of a single
parallel test circuit 700 is increased. For example, as more DUT
I/O blocks 704, 706, 708, 710 are coupled to a single channel I/O
block 702, it becomes more difficult to route signals between the
DUT I/O blocks 704, 706, 708, 710 and the channel I/O block 702
such that like signal propagation characteristics are maintained
amongst the different signal routes.
[0007] Even if the fan-out/fan-in of a single parallel test circuit
can be increased while maintaining signal integrity, there are
applications in which this might not be desirable. For example, a
parallel test circuit with increased fan-out/fan-in may be less
useful, or even cost-prohibitive, in applications where the
increased fan-out/fan-in is not always needed (or not needed at
all). As a result, it sometimes desirable to balance 1) the
increased fan-out/fan-in needs of some applications, with 2) the
modularity that lower order fan-out/fan-in circuits provide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Illustrative embodiments of the invention are illustrated in
the drawings, in which:
[0009] FIG. 1 illustrates exemplary apparatus for transmitting
signals between at least three transmit/receive units, each of
which is coupled to a transmission line network;
[0010] FIG. 2 illustrates an exemplary method for transmitting
signals between at least three transmit/receive units coupled to a
transmission line network;
[0011] FIG. 3 illustrates exemplary apparatus for implementing the
method shown in FIG. 2;
[0012] FIG. 4 illustrates an exemplary implementation of one of the
switching elements shown in FIG. 3, as well as an exemplary way in
which the control system shown in FIG. 3 may be coupled with the
switching element;
[0013] FIG. 5 illustrates in more detail how the transmit/receive
unit of one of the parallel test circuits shown in FIG. 1 may be
configured;
[0014] FIG. 6 illustrates an exemplary way to configure the
transmit/receive unit of each parallel test circuit shown in FIG.
1, so that the signal delay between the parallel test circuits may
be adjusted; and
[0015] FIG. 7 provides a high-level representation of an exemplary
parallel test circuit.
DETAILED DESCRIPTION
[0016] Disclosed herein are methods and apparatus for transmitting
signals between at least three transmit/receive units, each of
which is coupled to a transmission line network. In some
embodiments, the methods and apparatus can be used to
fan-out/fan-in a fully bi-directional signal path by two (i.e., 1:2
or 2:1). See, for example, the exemplary apparatus 100 shown in
FIG. 1. The apparatus 100 comprises a test system 102 coupled to
each of two parallel test circuits 106, 108. Each of the parallel
test circuits 106, 108 may be constructed as described in the '378
application, or in other ways. Each of the test system 102 and the
parallel test circuits 106, 108 comprises a transmit/receive unit
110, 112, 114 that couples a respective one of the test system 102
and parallel test circuits 106, 108 to a transmission line network
104. If each of the parallel test circuits 106, 108
fans-in/fans-out a signal by four (i.e., 1:4 or 4:1), the test
system 100 may provide a single test signal to an array of up to
eight device under test input/outputs (DUT I/Os) 116. If the
transmit/receive unit 112, 114 of each parallel test circuit 106,
108 is coupled to an active driver "per DUT I/O" (i.e., similarly
to what is shown in FIG. 7), and if the active drivers per DUT I/O
are individually controllable (i.e., each is able to be placed in
an ON or OFF state), then the test system 102 may provide a single
test signal to any one or combination of the DUT I/Os 116.
Similarly, in a reverse flow through the apparatus 100, the test
system 102 may receive signals from any of the DUT I/Os 116.
[0017] Although FIG. 1 illustrates exemplary apparatus 100 having
three transmit/receive units 110, 112, 114 coupled to a
transmission line network 104, the methods and apparatus disclosed
herein may be used to couple more or fewer (for example, two)
transmit/receive units to a transmission line network. This said,
the methods and apparatus disclosed are particularly suited for
networks requiring an increase in fan-out and fan-in by two.
[0018] In the above context, FIG. 2 illustrates an exemplary method
200 for transmitting signals between at least three
transmit/receive units coupled to a transmission line network. The
method comprises, for each signal transmission over the
transmission line network, designating one of the transmit/receive
units as a transmitting unit and designating all other ones of the
transmit/receive units as non-transmitting units (at block 202).
The method 200 further comprises, for each of at least two
different signal transmissions over the transmission line network,
1) designating a different one of the transmit/receive units as the
transmitting unit (at block 204), 2) actively terminating the
transmission line network using at least one of the
non-transmitting units (at block 206), 3) transmitting a signal
over the transmission line network, the sigal being transmitted
from the transmitting unit (at block 208), and 4) receiving the
transmitted signal at one or more of the non-transmitting units (at
block 210). The transmission line network is actively terminated by
driving a DC voltage through an active driver of a non-transmitting
unit, which active driver has an output that is coupled to the
transmission line network via a termination resistor. Typically,
but not necessarily, all of the non-transmitting units will be
configured to terminate the transmission line.
[0019] When the non-transmitting units coupled to transmission line
network are actively terminated, signals may be transmitted by a
transmitting unit, and received by one or more of the
non-transmitting units, with good signal integrity. And by
selectively enabling and disabling the active termination provided
by transmit/receive units, depending one whether they are
configured as a transmitting or non-transmitting unit during a
particular signal transmission, signals may be transmitted with
good signal integrity in any direction over the transmission line
network.
[0020] The exemplary method 200 can be better understood by
referring to exemplary apparatus for implementing the method 300.
One exemplary collection 300 of apparatus is shown in FIG. 3, in
which three transmit/receive units 302, 304, 306 are respectively
coupled to three input/output (I/O) terminals 308, 310, 312 of a
transmission line network 314. In FIG. 3, the elements that move
signals toward the transmission line network are referred to as
"drivers", and the elements that move signals away from the
transmission line network are referred to as "receivers". With this
convention in mind, each of the transmit/receive units comprises an
active receiver 316, an active driver 318, a termination resistor
320, and a switching element 322. Each of the active receivers 316
has a receiver input 324 coupled to a respective one of the I/O
terminals 308. Each of the active drivers 318 has a driver input
326 coupled to a driver output 328. A termination resistor 320
couples the driver output 328 to a respective one of the I/O
terminals 308. The switching element 322 is configured to
selectively couple the driver input 326 to a DC voltage source 330.
The switching element 322 may also be configured to selectively
couple the driver input 326 to a signal source 332.
[0021] A control system 334 may be coupled to, or integrated with,
the apparatus 300. The control system 334 couples to the switching
elements 322 of the at least three transmit/receive units 302, 304,
306 and configures the switching elements 322 to A) couple the
driver input 326 and signal source 332 of a transmitting one 302 of
the transmit/receive units, and B) couple the driver input 326 and
DC voltage source 330 of at least one non-transmitting one 304, 306
of the transmit/receive units.
[0022] FIG. 4 illustrates an exemplary implementation of one of the
switching elements 322, as well as an exemplary way in which the
control system 334 may be coupled with the switching element 322.
By way of example, the switching element 322 is shown to comprise a
multiplexer 400 having first and second multiplexer inputs (labeled
"1" and "0"), a multiplexer output coupled to the driver input 326,
and a select input (labeled "SEL"). The DC voltage source 330 is
coupled to the first multiplexer input, and the signal source 332
is coupled to the second multiplexer input. The control system 334
is coupled to the select input of the multiplexer 400. During use
of the transmit/receive unit 302, the control system 334 may
configure the multiplexer 400 to couple the driver input 326 and
signal source 332 (i.e., when the transmit/receive unit 302 is
configured as a transmitting unit), and B) couple the driver input
326 and the DC voltage source 330 (i.e., when the transmit/receive
unit 302 is configured as a non-transmitting unit). If each of the
transmit/receive units 302, 304, 306 shown in FIG. 3 is constructed
similarly to the transmit/receive unit 302 shown in FIG. 4, the
control system 334 may also be configured to A) couple the driver
input and signal source of any transmit/receive unit that is
designated a transmitting unit, and B) couple the driver input and
DC voltage source of any transmit/receive unit that is designated a
non-transmitting unit.
[0023] Referring back to FIG. 1, FIG. 1 illustrates how the
transmission line network shown in FIG. 3 can be used to fan-out a
single test channel of a test system 102 (e.g., a circuit tester)
to two of the parallel test circuits 106, 108 disclosed in the '378
application (and ultimately, to a plurality of DUT I/Os 116).
Depending on a desired direction of data flow over the transmission
line network 104, a control system such as the one disclosed in
FIGS. 3 and 4 may be configured to 1) dynamically place each of the
transmit/receive units 110, 112, 114 in a transmit mode or a
receive mode, and 2) dynamically enable and disable an active
termination of each transmit/receive unit 110, 112, 114.
[0024] FIG. 5 illustrates in more detail how the transmit/receive
unit 112, 114 of one of the parallel test circuits 106, 108 shown
in FIG. 1 may be configured. Note that the transmit/receive unit
500 (FIG. 5) is in many ways configured similarly to the generic
transmit/receive unit 302 shown in FIG. 4. However, the control
system 502, 504 shown in FIG. 5 is more robust, for providing some
of the additional functionality disclosed in the '378
application.
[0025] Note that the driver 506 in FIG. 5, labeled "Transmit
Buffer", moves signals away from the TESTER_IO node, toward one or
more DUT_IO nodes coupled to TRN_IN. The receiver 508, labeled
"Receive Buffer", moves signals from one of the DUT IO nodes
coupled to RCV_IN, toward the TESTER_IO node.
[0026] The control system 502, 504 shown in FIG. 5 receives a
plurality of signals (CHIO_TXBUF_ENA, CHIO_LOW_LEAK,
CHIO_VTERM_ENA, CHIO_CMP_MD, IO_MODE, CHIO_RCVMD, DRV/RCV). Some or
all of these signals may be provided to a parallel test circuit by,
for example, a test system such as the test system 102 (see FIG.
1). By controlling these various signals, the transmit/receive unit
500 may be placed in a number of different modes, including: Drive,
Receive and Low Leakage modes. Note that, for purposes of this
description, "Drive" mode is indicative of a data flow where a test
system is driving data to DUT I/Os through the parallel test
circuit 500, and "Receive" mode is indicative of a data flow where
the test system is receiving data from DUT I/Os through the
parallel test circuit 500.
[0027] Drive mode can be selected by setting IO_MODE=1 (for
Drive-only mode), or by setting IO_MODE=0 and DRV_RCV=1 (to Drive
in bi-directional mode). In Drive mode, the Transmit Buffer 506
receives a signal from a test system (a tester) via TESTER_IO,
buffers it, and distributes it to all DUT I/O drivers (referred to
as DUT_IO drivers in the '378 application). Input termination can
be ON or OFF, as controlled by CHIO_VTERM_ENA. When the termination
is enabled, the Receive Buffer 508 is turned ON and the Receiver
Buffer's source will be CHIO _VT, which is a termination voltage.
When the termination is disabled, the Receive Buffer 508 is turned
OFF.
[0028] Receive mode can be selected by setting IO_MODE=0 and
DRV_RCV=0 (to Receive in bi-directional mode), or by setting
IO_MODE=2 (when in ECRD compare mode). ECRD compare mode is
described later in this description. CHIO_VTERM_ENA has no effect
on termination in either of the receive modes.
[0029] The bidirectional receive mode may also be referred to as a
"Bypass" mode. Bypass mode is further enabled by setting
CHIO_RCVMD=0 and CHIO_VTERM_ENA=0. When this mode is
selected/enabled, one of the RCV_OUT signals is coupled to the
input of the Receive Buffer 508 through the multiplexers 510 and
512, enabling RCV_OUT to drive the TESTER_IO node. At any point in
time, RCV_OUT originates from one of the DUT I/Os, as determined by
RCV_BUF_SEL. By serially coupling the TESTER_IO node to the
different RCV_OUT signals, various DUT I/O signals can be serially
output to a test system coupled to the TESTER_IO node.
[0030] The ECRD compare mode is further enabled by setting
CHIO_RCVMD=1 and CHIO_VTERM_ENA=0. When this mode is
selected/enabled, one of the ECRD signals is coupled to the input
of the Receiver Buffer 508 through the multiplexers 510 and 514,
enabling ECRD to drive the TESTER_IO node. At any point in time,
ECRD originates from one of a plurality of comparators, as
determined by ECRDS. Each of the comparators (not shown) compares
one of the DUT I/O signals to an expected DUT I/O signal and
generates one of the ECRD signals.
[0031] Note that the Transmit Buffer 506 is controlled separately
by CHIO_TXBUF_ENA. Although the Transmit Buffer 506 could be left
ON all the time, thereby obviating the need for a CHIO_TXBUF_ENA
signal, it can be desirable to turn the Transmit Buffer 506 OFF
when driving ECRD signals to the TESTER_IO node. Turning the
Transmit Buffer 506 OFF in ECRD mode mitigates signal feedback
being picked up by the transmit/receive unit 500. It is desirable,
however, to turn the Transmit Buffer 506 ON when driving RCV_OUT
signals to the TESTER_IO node. This eliminates the existence of a
non-terminated stub on the transmission line network coupled to the
TESTER_IO node.
[0032] Low leakage mode can be selected by setting CHIO_LOW_LEAK=1.
In low leakage mode, the overall leakage at the TESTER_IO node goes
to <5 nA (nanoAmps).
[0033] The exemplary transmission line networks discussed so far
(see, FIGS. 1 and 3) have been coupled to only three
transmit/receive units, and as shown in FIG. 3, each
transmit/receive unit 302, 304, 306 is coupled to its own
transmission line segment 336, 338, 340, with all of the
transmission line segments 336, 338, 340 being coupled to a common
branch node 342. In other embodiments, a transmission line network
could be coupled to more or fewer transmit/receive units.
Preferably, a transmission line network is extended by branching
more transmission line segments from a common branch node. However,
it is also possible to add an additional branch node or nodes to a
transmission line network, or to couple two or more
transmit/receive units to a single transmission line segment. Doing
so, however, may require transmit/receive units to provide
different amounts of compensation for signal delay and other
factors. Also, the attachment of multiple transmit/receive units to
a single transmission line segment, or the addition of branch nodes
to a transmission line network, may lead to more signal degradation
at some or all of the transmit/receive units coupled to the
transmission line network (e.g., because of the increased impact of
the resistive divider created by the additional transmission line
branching).
[0034] In some embodiments, each of the transmission line segments
in a transmission line network (such as one of the networks 104,
314 shown in FIG. 1 or 3) is configured to have the same
characteristic impedance. So long as the receivers of
non-transmitting units are actively terminated, there is no need to
step the characteristic impedances of different segments based on
an expected direction of data flow over a transmission line
network.
[0035] By way of example, each of the transmission line segments in
a transmission line network may have a characteristic impedance of
50 Ohms. 50 Ohms is a useful characteristic impedance because 50
Ohm transmission lines are commonplace in today's communications
networks. However, the methods and apparatus disclosed herein are
not limited to use with 50 Ohm transmission line segments. In
particular applications, transmission line segments having other
characteristic impedances may be useful.
[0036] FIG. 6 illustrates an exemplary way to configure the
transmit/receive unit 112, 114 of each parallel test circuit 106,
108 shown in FIG. 1, so that the signal delay between the parallel
test circuits 106, 108 can be adjusted. As shown, each of the
parallel test circuits 106, 108 is provided with an adjustable
delay element 600, 602; and an input of each adjustable delay
element 600, 602 is coupled to a respective receiver output 604,
606 of one of the transmit/receive units 106, 108. To adjust the
signal delay between the parallel test circuits 106, 108, one of
the active drivers 608, 610 may be opened at a time, and
time-domain reflectometry (TDR) may be used to calculate the
round-trip signal delay from the test system 102 to one of the
parallel test circuits 106, 108. In some cases, the output of each
adjustable delay element 600, 602 may be coupled to the inputs of a
plurality of drivers, which drivers increase the signal fan-out of
a parallel test circuit 106, 108 (as described in the '378
application, and as shown in FIG. 7). In such a case, TDR may be
used to calculate the round-trip signal delay to the DUT I/O
drivers. Alternately, one of the drivers may be opened at a time,
and TDR may be used to calculate the round-trip signal delay to
each of a plurality of DUT I/Os. In this latter case, the delay of
an adjustable delay element 600 or 602 may be set based on an
average of the round-trip signal delays; based on a longest or
shortest round-trip signal delay; or based on other metrics. A
delay controller, which may in some cases be part of control system
334 (FIG. 3) may be configured to adjust the delays of the first
and second adjustable delay elements 600, 602. By way of example,
the delay controller may be integrated with the test system
102.
[0037] The methods and apparatus disclosed herein can be
advantageously employed in many applications. However, one
application in which they are particularly useful is test and
measurement. If the apparatus shown in FIG. 1 is incorporated into
a test and measurement environment, the active driver of the
transmit/receive unit 110 may be configured to transmit signals
carrying timing and voltage information over the transmission line
network 104, and the transmission line network 104 can 1) split the
signals, and 2) provide the signals to the transmit/receive units
112, 114 of the parallel test circuits 106, 108. In reverse, the
active drivers of the transmit/receiver units 112, 114 in the
parallel test circuits 106, 108 can, one at a time, be configured
to transmit signals carrying timing and voltage information over
the transmission line network 104. The signals transmitted by the
parallel test circuits 106, 108 can then be received by the test
system 102. In either direction, signals transmitted over the
transmission line network can be transmitted and received with good
integrity, in part because of the active termination of the network
by any transmit/receive unit that is not transmitting.
* * * * *